Process for preparing photographic emulsions



United States Patent assignor to N.Y., a cor- The present invention relates to the processing of gelatin photographic emulsions, more particularly toan improved method for washing out soluble salts from such emulsions.

In the preparation of a photographic, light-sensitive emulsion the sensitive substance is usually a silver halide. This material is prepared by addition of a soluble silver salt to a soluble halide such as potassium or ammonium halide. In the resulting double decomposition or chemical interchange, one product is the desired insoluble silver halide and the other is the undesired solublesalt e.g. potassium nitrate. The stability and sensitivity of the emulsion are largely controlled by the presence of some protective colloid, usually gelatin, during the precipitation of the insoluble silver halide. A stable suspension is thus formed.

There are likewise formed in this reaction soluble inorganic salts that must be removed from the gelatin prior to further treatment and coating it upon photographic plates or film. Many methods for washing out these superfluous salts have been developed. In some processes the gelatin suspension is gelled, then extruded or cut into fine shreds and subjected to a washing treatment which may last from 2 to 4 hours. Such methods are cumbersome, slow, and, therefore, inefficient. In addition, such washing offers the opportunity for the introduction of impurities from the water used in washing the gelatin emulsion.

Heretofo-renitrates of metals of group four of the periodic table, which includes tin, lead, titanium, cerium, thorium, zirconium, germanium, etc., have been tried in an attempt to rid the precipitated emulsion of undesired soluble impurities. These salts typified for example by zirconium nitrate, Zr(No are ordinary binary salts wherein the metal is in quadrivalent form in the cation. It is a characteristic of these salts that the metal, under the influence of an electrolytic field, migrates to the cathode. It is believed that the effectiveness of such materials to the extent that they are effective resides primarily in their capacity to precipitate the colloidal silver halide which carries with it the protective colloid, the gelatin. These prior art processes require very careful control of the operating conditions since such conditions, for example, gelatin concentration and temperature, are extremely critical. The gelatin concentration must be relatively low, say 1% and the temperature of the emulsion at the time of precipitating silver halide must be likewise low, say 50-70 F. Such low temperatures cannot be employed with gelatin emulsions containing, for example, of gelatin because gelation would occur. Moreover, the precipitation brought about by the use of thorium salts and salts of other group IV cations requires a period of about 2-4 hours. In addition to the above disadvantage, the cations of group IV interfere with the properties of the photographic emulsions in that they are for the most part desensitizers, reducing the speed of the emulsions, and in some cases are fogging agents. Also, thorium is reported to be radioactive so that it would cause fogging of the emulsion and otherwise adversely affecting its shelf-life.

Thus, because of these numerous defects including the peculiar sensitivity to temperature and concentration and because of the extremely slow reaction time, the use of these dewatering materials has been impractical.

Other methods for dewatering gelatin in connection with the washing of emulsions include treatment with dehydrating salts or alcohols. Such salts include ammonium, sodium, potassium and magnesium sulfates, chlorides, nitrates, and the like, which must be used in extremely high concentrations requiring in turn extensive washing of the dewatered precipitate for their removal. While alcohols, acetone, and like organic solvents may be employed in dewatering the gelatin, these, too, require prohibitive quantities making the operation in this case extremely costly and presenting a fire hazard. Also, dodecyl sulfate has been employed in the same manner and although highly effective in dewatering the gelatin it has a serious drawback in that it cannot be removed from the gelatin precipitate by conventional washing techniques. Its removal requires washing with alcohol with aforementioned disadvantages.

It is the object of the present invention to provide a method which will overcome many of the disadvantages of the former processes for washing and purifying the gelatin photographic suspensions. Other objects will be apparent to those skilled-in-the-art.

It has now been found that the washing of gelatin photographic emulsions is greatly facilitated by using a basic zirconium sulfate to precipitate the gelatin serving as a protective colloid. The gelatin takes down with it the silver halide and leaves the bulk of the soluble salts in the supernatant liquor. In addition, it is an easy matter to remove the soluble salts still remaining in the gelatin. This may be done simply by a few washings using either decantation or filtration.

The manner in which the basic zirconium sulfate is employed in the present invention involves first reducing the pH of the gelatin photographic emulsion to, say, about 4.5 and elevating its temperature to, say about -140 F., adding a dilute solution of the basic zirconium sulfate to dewater and precipitate the. gelatin. The gelatin containing the silver halides is separated from the supernatant liquor by decantation, filtration, centn'fugation, or the like, and is easily washed free from any soluble salts that may have been occluded, using water at, say, 50 F. The washed gelatin is then suspended in water at a pH of, say, about 6.8 or above and preferably at a temperature of, say, about 100-140 F. Said solution may contain or there may be later added to it a hydroxy carboxylic acid or a salt thereof of relatively low molecular weight capable of forming a soluble complex with the precipitate. Such acids and salts include citric acid, gluconic acid and tartaric acid and their soluble salts. The resolubilized gelatin emulsion is then treated in the usual manner for the further processing of such emulsion preparatory to being coated on paper, plates, plastic films such as polyester, cellulose acetate, and the like.

According to certain aspects of this invention, a photographic gelatin emulsion which is free of undesired soluble salts may be prepared from a photographic gelatin emulsion containing insoluble silver halide together with impurities including soluble salts by the process which comprises reducing the pH of said emulsion to below the isoelectric pH of the gelatin, adding to the emulsion a dilute solution of basic zirconium sulphate thereby dewatering and precipitating said gelatin which carries down with it the insoluble silver halide leaving the bulk of the soluble salt impurities in the supernatant liquor, separating the precipitated gelatin from said liquor, washing said gelatin precipitate to remove soluble salts therefrom, suspending said precipitate in water at a pH above said isoelectric point, said water containing in solution a hydroxy carboxylic organic acid ion of low molecular weight which forms a soluble complex thereby resolubilizing the gelatin and reforming the emulsion.

Generally, gelatin prepared from limed stocks is preferred for use in preparing photographic emulsions although it is also possible to employ gelatin extracted from pigskins. The liming process removes various impurities which would otherwise interfere with the photographic properties of the emulsion and the processing of pigskins does not provide this effect. In adjusting the pH of the emulsion prior to adding the basic zirconium sulfate solution, the adjustment should be to a pH below the iso electric point of the gelatin which in the case of limed skins is about 4.75-4.9. As is well known, the tendency of gelatin to precipitate is increased by adjusting its pH below its isoelectric point.

While the isoelectric point of the gelatin extracted from pigs'kins is much higher than that extracted from materials that have been limed, generally being about 7.9, but sometimes as low as 6.5, nevertheless, the so-called pig gelatin may be dewatered and resolubilized using the same pH conditions described for gelatin from limed stocks.

The basic zirconium sulfate which is employed in the practice of this invention to dewater and precipitate the gelatin, is distinguished by its unique chemical nature which renders it characteristically different from other zirconium compositions. The chemical formula of basic zirconium sulfate (to the extent that it is possible to represent it) may be: ZrO(SO More accurately, the

formula of basic zirconium sulfate in aqueous acidic solution has been said to be: H (OZr(SO ).3H O.

Among the chemical reasons for this unusual formulation may be noted the fact that if a solution of basic zirconium sulfate be subjected to electrolytic action, the zirconium may be found at the anode, in the form of the anion ZrO(SO In contrast, if a solution of any other zirconium salt e.g. zirconium nitrate or chloride be subjected to electrolysis the salt e.g. Zr(NO will dissociate and the cation Zr will be found at the cathode as would normally be expected.

In any event, these formulae and explanations are attempts to explain the well-known phenomenon that solutions of zirconium sulfate do not give the characteristic reactions exhibited by the chloride or the nitrate. It may be noted that because of this unique feature, basic zirconium sulfate, i.e. zirconium sulfate in water, has been referred to as sulfatozirconic acid. Regardless of the precise chemical structure of basic zirconium sulfates,

they are widely recognized as being completely different from other zirconium salts.

The basic zirconium sulfate solution is very acid; for example, the solution generally employed has a pH of 1.40. Hence, upon the addition of the zirconium salt solution to e.g. a 10% gelatin emulsion, the pH of which has been adjusted to about 4.5, the pH of said emulsion drops considerably reaching values as low as 3.0, and in the case of emulsions containing less gelatin, say, 1%, which are therefore less buffered, the pH may drop as low as 2.5. The pH of the emulsion must be carefully controlled, depending upon the composition of the photographic emulsion, in order to avoid its having an adverse effect upon the photographic properties of the emulsion, but, generally, the pH changes discussed above may be employed without adverse effect.

The basic zirconium sulfate may be employed in aqueous solution of varying concentrations, and generally a 10% solution may be used. The amount of zirconium salt (dry basis) employed in precipitating the gelatin is preferably of the order of 2575% by weight of the gelatin (dry basis) contained in the emulsion. The use of larger quantities of the zirconium salt served no useful purpose, and in fact require additional washing for their removal.

The precipitation effected by the addition of the basic zirconium sulfate may occur at any temperature below 200 B, it being preferred the temperature range be about -140 F. Lowering the temperature should be avoided where the concentration of gelatin in the emulsion is relatively high, say, 10%, since gelation may occur if the temperature is too low. Precipitation of the gelatin at a temperature between 6080 F. leads to a looser, less gummy precipitate which can be readily broken up by stirring and, due to its greater surface area, can be more readily Washed and redissolved than a precipitate from a hot solution. On the other hand, a precipitate from a hot emulsion is much less voluminous and, therefore, occludes less mother liquor and requires less washing. Also, it hardens on cooling, is easily broken up and acn, therefore, be washed as easily as a precipitate from a cold emulsion.

Upon addition of the basic zirconium sulfate to the emulsion, the gelatin is dewatered and precipitates carrying down with it the insoluble silver halide i.e. silver bromo-iodide. It is a feature of this invention that the bulk of the undesirable soluble salts remain in the supernatant liquor.

The precipitated or denatured gelatin-silver halide emulsion may be separated from the supernatant liquor by filtration or decantation. It is then washed, preferably with distilled water. The temperature of washing the precipitate is preferably relatively low, generally about 5060 F. Washing may be effected continuously or batchwise and may include, prior to the last washing, one or more washings with sodium bicarbonate.

The washed precipitated emulsion will be found to be substantially free of undesirable soluble salts because of the hereinbefore noted pretreatment. It is a feature of this invention that the so-washed precipitate may be readily resolubilized.

Resolubilization of the washed emulsion may be effected by suspending it in water at a pH above its isoelectric point. The optimum pH of the suspended gelatin precipitate for the purpose of resolubilizing the gelatin is preferably about 6.8 which, of course, is above isoelectric point. The pH need not be adjusted as high as this to permit solubilization but this pH is preferred for hastening resolubilization. Also, higher pI-Is may be employed but are avoided for the most part because of the possibility of adverse effect on the photographic salts.

The temperature of the water used in solubilizing the gelatin precipitate is best maintained relatively high, say, about 100 F. Lower temperatures may be employed but more time for resolubilization is required. Temperatures in excess of 'F. can result in some deterioration of the photographic properties of the emulsion because of the relatively high pHs usually employed at this stage of the process.

The water in which the emulsion is to be solubilized contains a low molecular weight hydroxy polycarboxylic organic acid anion. Preferably the acid will be an aliphatic acid typified by citric acid, gluconic acid, and tartaric acid and it may be employed in the form of a soluble salt e.g. the ammonium salt, the alkali metal salts, the amine salts e.g. of monoethanolamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide, morpholine, N-ethylmorpholine, methylamine, piperidine, etc.

When the acid employed is an aromatic acid e.g. salicylic acid, the dissolving technique to be used includes addition of the acid to the precipitated gelatin, adjustment of the pH to about 6.5 as by addition of an alkali including the above-noted organic bases, and heating to above the melting point of the gelatin.

The resolubilized gelatin-silver halide emulsion may be used as desired in preparation of desired photographic products.

It is a feature of this invention that this technique for obtaining gelatin-containing emulsions which are free of undesired salts can be employed over a wide range of conditions. For example, emulsions containing as little as 0.3% (or less) gelatin or as much as 15% gelatin can be handled. It may be noted that prior art processes using e.g. zirconium nitrate will not give satisfactory results on emulsions having gelatin concentrations over such a wide range.

Prior art processes are also characterized in requiring low temperatures (e.g. 10-20 C.) which would gel an emulsion containing gelatin in any substantial concentration, whereas the process of the instant invention operates over a wide range of temperature. Furthermore prior art coagulations or precipitations may require from two to four hours whereas the process of the instant invention is instantaneous. This latter, aside from being a significant improvement in practical operations, clearly demonstrates that the new technique is inherently different from prior techniques.

Typical examples of the process of the present invention are set forth below.

Example I A so-called boiling emulsion for use in making photo graphic negatives is prepared as follows:

Prepare a 10% basic zirconium sulfate solution by dissolving 100 g. of said salt in 900 g. of water with heating until all of the salt is dissolved.

Prepare an ammonium-goldthiocyanate solution by combining 6 cc. of a 1% gold chloride (HAuCl -3H O) solution and 50 cc. of a 1% ammonium-thiocyanate solu tion, allowing the solution to clear before using.

Prepare a gelatin solution containing 9 g. of gelatin, 80.5 g. of potassium bromide, g. of potassium iodide dissolved in 725 g. of distilled water.

Prepare a silver nitrate solution containing 100 g. of silver nitrate dissolved in 800 g. of distilled water.

While vigorously stirring the gelatin solution at 158 F. quickly add 300 cc. of the silver nitrate solution at the same temperature. 30 seconds later start adding the remaining 500 cc. in 100 cc. portions with stirring, allowing 10 minutes between each addition. Digest the completed emulsion for 20 minutes at 158 F. Allow the emulsion to cool to 100 F., add 0.5 cc. glacial acetic acid followed by 70 cc. of a 10% solution of basic zirconium sulfate, stirring until a heavy fiocculent precipitate occurs. Allow said precipitate to settle to the bottom and discard the supernatant liquor.

Wash the precipitate by pouring onto it 500 cc. of cold distilled water and stir for 5 minutes so that the precipitate is completely broken up. Repeat this washing operation five additional times, stirring 5 minutes with each addition. Give the precipitate a final washing by adding 500 cc. of cold distilled water containing 2 g. of sodium bicarbonate, allowing the precipitate to soak therein for one hour. Discard the supernatant bicarbonate solution. All of the wash water employed above should be at the temperature of about 50 F.

Cover the precipitate with 100 cc. of distilled water containing 5 g. sodium citrate in solution and allow the precipitate to soak at least minutes with frequent stirring. Heat the suspension to 131 F. and continue said heating until the precipitate is completely dissolved. Add 110 cc. of distilled water, mix thoroughly and pour 200 cc. of this final emulsion onto g. of test gelatin. Allow the gelatin to soak for 10-15 minutes for complete solution, add 0.5 cc. of the ammonium-gold-thiocyanate solution and digest the resulting solution at 140 F. until maximum speed just prior to fogging is reached.

Example II A so-called ammonia emulsion used in making photographic negatives is prepared as follows:

Prepare a gelatin solution containing g. of gelatin, 92 g. of potassium bromide, 2 g. of potassium iodide in 450 cc. of distilled water.

Prepare a silver nitrate solution containing 100 g. of

silver nitrate in 300 cc. of distilled water with sufficient ammonium hydroxide (25%) added to precipitate and redissolve Ag O and form the silver ammine.

Prepare a test gelatin solution containing 22.5 g. of gelatin in 75 cc. of distilled water.

With constant stirring add half of the silver nitrate solution at 104 F. to the gelatin solution at 104 F. Allow the solution to digest for 45 minutes at this temperature and then add the remainder of the silver nitrate solution. Cool the resulting emulsion to -100 F. and add 70 cc. of concentrated hydrochloric acid plus 35 cc. of glacial acetic acid, cooling again to F. Next add 145 cc. of a 10% solution of basic zirconium sulfate to the emulsion and stir until a heavy fiocculent precipitate is obtained. After allowing the precipitate to settle to the bottom, discard the supernatant liquor and wash the precipitate six times using 500 cc. of distilled water at about 50 F. and stirring 5 minutes each time before decanting. Give the precipitate a final wash with 500 cc. of cold distilled water with 2 g. of sodium bicarbonate in solution, allowing the precipitate to soak in this solution for one hour. Decant the bicarbonate solution and add 500 cc. of cold distilled water containing 15 'g. of sodium citrate in solution. Allow the precipitate to soak in this solution with frequent stirring for 15 minutes. Heat the precipitate in the sodium citrate solution to 131 F. and continue to heat the same at said temperature with frequent stirring until the precipitate is entirely in solution. Add 800 cc. of distilled water and mix thoroughly.

Add 200 cc. of this emulsion to the test gelatin solution prepared above and allow it to soak for 10-15 minutes after which time it is dissolved. Add 0.55 cc. of an ammonium-gold-thiocyanate solution such as that prepared in Example I and digest at 113-122 F. until maximum speed just prior to fogging is obtained.

Example [H An emulsion generally employed in photostating processes is prepared by the following procedure:

Prepare a solution containing 60 g. of gelatin, 23 g. of ammonium bromide, 0.5 g. of potassium iodide in 450 g. of distilled water.

Prepare a silver nitrate solution containing 38 g. of silver nitrate and 75 g. of distilled water with sufficient ammonium hydroxide (25%) added to precipitate and redissolve Ag O and form the silver amrnine.

Let the gelatin solution stand for at least 30 minutes and then heat the same to 115 F. Pour the silver nitrate solution at 99 F. into the gelatin solution with stirring. Cool the resulting solution to 8590 F., add 35 cc. of concentrated hydrochloric acid plus 5 cc. of glacial acetic acid and cool the solution to 85 90 F. Add 360 cc. of a 10% solution of basic zirconium sulfate with vigorous stirring until a heavy fiocculent precipitate is formed. After the precipitate has settled to the bottom discard the supernatant liquor and wash the precipitate by the addition of one liter of distilled water and stirring 45 minutes so that the precipitate is broken up as [fine as possible. Repeat this washing step five times and then wash the precipitate for the final time with one liter of distilled water containing 4 g. of sodium bicarbonate, allowing the precipitate to soak in this solution with frequent stirring for one hour. All of the wash water employed above should be at a temperature of about 50 F. Decant the sodium bicarbonate solution and add 400 cc. of cold distilled water containing in solution 35 g. of sodium citrate. Allow the precipitate to soak in this solution for at least 30 minutes with frequent stirring and then complete solution of the precipitate by raising the temperature of the sodium citrate solution to 115 F. Digest the reformed emulsion at 115 F. and after 30 minutes and one hour, respectively, prepare test coatings.

Zirconium sulfates of varying degrees of basicity may be produced, there being no definite molecular combination but simply a ratio between the sulfate and basic radicals. \Any basic zirconium sulfate can be used in the practice of the present invention and herein and in the attached claims the term a basic zirconium sulfate is intended to include all zirconium sulfates of any degree of basicity.

it will be apparent that these zirconium sulfates are readily distinguishable from other zirconium salts, including zirconium nitrate, by forming anionic complexes in comparison to the cationic nature of the other zirconium salts; by their ability to precipitate gelatin which carries down with it the other silver-halide components of the emulsion in comparison to the other zirconium salts which precipitate primarily the silver-halide; by their ability to precipitate a gelatin which can be readily resolubilized under the conditions herein disclosed in comparison to the other zirconium salts which would give a hardened, tanned, insoluble gelatin which is soluble only with great difficulty.

While the present invention has been described with reference to specific embodiments and operating details and conditions, it is not to be construed as limited thereby but reference is to be had to the appended claims for a definition of its scope. This application is a continuationin-part of application Serial No. 565,788, filed February 16, 1956, now abandoned, by the same inventor for Process.

What is claimed is:

1. The process of preparing a photographic gelatin emulsion which is free of undesired soluble salts from a photographic gelatin emulsion containing insoluble silver halide together with impurities including soluble salts which comprises reducing the pH of said emulsion to below the isoelectric pH of the gelatin, adding to the emulsion a dilute solution of basic zirconium sulfate thereby dewatering and precipitating said gelatin which carries down with it the insoluble silver halide leaving the bulk of the soluble salt impurities in the supernatant liquor, separating the precipitated gelatin from said liquor, washing said gelatin precipitate to remove soluble salts therefrom, suspending said precipitate in water at a pH above said isoelectric point, said water containing in solution a hydroxy carboxylic organic acid ion of low molecular weight which forms a soluble complex with the precipitate thereby resolubilizing the gelatin and reforming the emulsion.

2. In the processing of a photographic gelatin emulsion containing insoluble silver halide and also soluble salts as impurities, the improvement comprising adjusting the pH of-said emulsion to below 4.5, adding a dilute solution of a basic zirconium sulfate to dewater and precipitate the gelatin which carries down with it the insoluble silver halide leaving the bulk of any soluble salt in the supernatant liquor, separating the precipitated gelatin and said liquor, washing said gelatin precipitate to remove soluble salts therefrom, suspending said precipitate in water at a pH above 6.8, said water containing in solution an aliphatic hydroxy carboxylic organic acid ion of low molecular weight which forms a complex to resolubilize the gelatin and reform the emulsion.

3. In the processing ofa photographic gelatin emulsion containing insoluble silver halide and also soluble salts as impurities, the improvement comprising adjusting the pH of said emulsion to below 4.5, adding a dilute solution of a basic zirconium sulfate to dewater and precipitate the gelatin which carries down with it the insoluble silver halide leaving the bulk of any soluble salt in the supernatant liquor, separating the precipitated gelatin and said liquor, Washing said gelatin precipitate to remove soluble salts therefrom, suspending said precipitate in water at a pH above 6.8, said water containing in solution sodium citrate which forms a complex to resolubilize the gelatin and reform the emulsion.

4. In the processing of a photographic gelatin emulsion containing insoluble silver halide and also soluble salts as impurities, the improvement comprising adjusting the pH of said emulsion to below 4.5, adding about a 10% solution of a basic zirconium sulfate in such an amount that the added zirconium salt equals about 25-75% of the gelatin contained in the emulsion to dewater and precipitate the gelatin which carries down with it the insoluble silver halide leaving the bulk of any soluble salt in the supernatant liquor, separating the precipitated gelatin and said liquor, washing said gelatin precipitate to remove soluble salts there-from, suspending said pre cipitate in water at a pH above 6.8, said water containing in solution sodium citrate which forms a complex to resolubilize the gelatin and reform the emulsion.

5. In the processing of a photographic gelatin emulsion containing insoluble silver halide and also soluble salts as impurities, the improvement comprising adjusting the pH of said emulsion to below 4.5, adding about a 10% solution of a basic zirocnium sulfate in such an amount that the added zirconium salt equals about 25-75% of the gelatin contained in the emulsion to dewater and precipitate the gelatin which carries down with it the insoluble silver halide leaving the bulk of any soluble salt in the supernatant liquor, separating the precipitated gelatin and said liquor, washing said gelatin precipitate with water at about 50-60 F. to remove soluble salts therefrom, suspending said precipitate in water at about F. at a pH above 6.8, said water containing in solution sodium citrate which forms a complex to resolubilize the gelatin and reform the emulsion.

References Cited in the file of this patent UNITED STATES PATENTS 1,844,716 Lambert Feb. 9, .1932 2,327,004 Wadman Aug. 17, 1943 2,489,341 Waller et a1. Nov. 29, 1949 2,618,556 Hewitson et al Nov. 18, 1952 

1. THE PROCESS OF PREPARING A PHOTOGRAPHIC GELATIN EMULSION WHICH IS FREE OF UNDESIRED SOLUBLE SALTS FROM A PHOTOGRAPHIC GELATIN EMULSION CONTAINING INSOLUBLE SILVER HALIDE TOGETHER WITH IMPURITIES INCLUDING SOLUBLE SALTS WHICH COMPRISES REDUCING THE PH OF SAID EMULSION TO BELOW THE ISOELECTRIC PH OF THE GELATIN, ADDING TO THE EMULSION A DILUTE SOLUTION OF BASIC ZIRCONIUM SULFATE THEREBY DEWATERING AND PRECIPITATING SAID GELATIN WHICH CARRIES DOWN WITH IT THE INSOLUBLE SILVER HALIDE LEAVING THE BULK OF THE SOLUBLE SALT IMPURITIES IN THE SUPERNATANT LIQUOR, SEPARATING THE PRECIPITATED GELATIN FROM SAID LIQUOR, WASHING SAID GELATIN PRECIPITATE TO REMOVE SOLUBLE SALTS THEREFROM, SUSPENDING SAID PRECIPITATE IN WATER AT A PH ABOVE SAID ISOELECTRIC POINT, SAID WATER CONTAINING IN SOLUTION A HYDROXY CARBOXYLIC ORGANIC ACID ION OF LOW MOLECULAR WEIGHT WHICH FORMS A SOLUBLE COMPLEX WITH THE PRECIPITATE THEREBY RESOLUBILIZING THE GELATIN AND REFORMING THE EMULSION. 